ext2fs: general cleanup.

ext2fs:	general cleanup.

- Remove unused extern declarations in fs.h
- Correct comments in ext2_dir.h
- Several panic() messages showed wrong function names.
- Remove commented out stray line in ext2_alloc.c.
- Remove the unused macro EXT2_BLOCK_SIZE_BITS() and the then
  write-only member e2fs_blocksize_bits from struct m_ext2fs.
- Remove the unused macro EXT2_FIRST_INO() and the then write-only
  member e2fs_first_inode from struct m_ext2fs.
- Remove EXT2_DESC_PER_BLOCK() and the member e2fs_descpb from
  struct m_ext2fs.
- Remove the unused members e2fs_bmask, e2fs_dbpg and
  e2fs_mount_opt from struct m_ext2fs
- Correct harmless off-by-one error for fspath in ext2_vfsops.c.
- Remove the unused and broken macros EXT2_ADDR_PER_BLOCK_BITS()
  and EXT2_DESC_PER_BLOCK_BITS().
- Remove the !_KERNEL versions of the EXT2_* macros.

Submitted by:	Christoph Mallon
MFC after:	2 weeks